1957 Pickup Trim Codes?

[rdwhite01]

Hello everyone, I just joined this forum a couple of days ago and look forward to using it. I am the second owner of a 1957 Custom Cab C3100 and when inspecting the weight tag on the lower drivers side door post I noticed that the Gross Weight Tag had paint and trim code numbers. I have found the paint color to match the paint number, but I have not been able to locate a description of the trim number, which is #4318. Would anyone know what these trim numbers stand for. I have received the Chevy Restoration Package and it did not include the trim number information. Thanks in advance for any help.